Referring to FIGS. 1 and 2, granted U.S. Pat. No. 6,342,270 B1 discloses a process for manufacturing a hydrostatic bearing 10 of porous material. A base member 1 is placed in a housing 3, a gel is applied on an exposed surface 11 of the base member 1, and baked thereon, thus forming a surface restrictor layer 2 sealing the exposed surface 11. Air is supplied into the housing 3 during grinding the surface restrictor layer 2 by using a grinding wheel in order to measure the flow rate of the air from the surface restrictor layer 2.
The surface restrictor layer 2 is pushed by the air flowing through the base member 1 so as to be separated from the base member 1 easily. Moreover, the surface restrictor layer 2 exposed by the housing 3 is grinded and the air is supplied into the housing 3 in the grinding process such that partial base member 1 and partial surface restrictor layer 2 may be removed by grinding if the surface restrictor layer 2 is distributed on the exposed surface 11 of the base member 1 unevenly. Consequently, the flow rate of the air permeating through the hydrostatic bearing 10 may be sufficient but not even.
On the other hand, it is not easy to control the thickness of the gel penetrating into the base member 1 during mass production of the hydrostatic bearings 10, for this reason, the surface restrictor layers 2 formed by baking the gel may have different thicknesses, and after grinding, the surface restrictor layers 2 on different base member 1 may cause the hydrostatic bearings 10 have different exhaust distributions. Pneumatic hammer may occur if the hydrostatic bearings 10 having different exhaust distributions are mounted on platform.